The present invention relates to polyarylene sulfide resin compositions. More particularly, the present invention is concerned with polyarylene sulfide resin compositions which provide molded articles thereof with remarkably improved resistance to discoloration.
In recent years, thermoplastic resins having a combination of excellent mechanical properties, high heat resistance and high chemical resistance with flame retardance have been desired as materials for electrical and electronic equipment components, automobile equipment components, and chemical equipment components.
Polyarylene sulfide resin including polyphenylene sulfide is one of the resins capable of meeting this desire. The demand for polyarylene sulfide has expanded because such resins possess excellent properties for the cost.
However, polyarylene sulfide resin exhibits many unfavorable phenomena relative to appearance when processed by injection molding. For example, problems including changes in the hue of polyarylene sulfide molded articles as a whole in comparison with the hue before molding, the occurrence of black stripes or mottled discoloration, and a high susceptibility to discoloration during use of the molded articles at high temperature, all hereinafter simply referred to as "discoloration", have resulted. In order to solve these discoloration problems, Japanese Patent Laid-Open No. 1735/1972) proposed to add an organic phosphite to the polyarylene sulfide resin. However, this method has been found to yield various problems. Specifically, the heat resistance of the phosphite additive is poor and an evaporation gas or a decomposition gas is liable to occur during molding. Accordingly, addition of a phosphite has not been regarded as satisfactory in respect to the processing, properties, and appearance of polyarylene sulfide molded articles.